Is Fasting necessary?

(Juanita Rice) #1

Hi, I’m new here. This is my first post. I’ve been lurking here for a couple of weeks. I started Keto 18 days ago staying under 20 grams of carbs. I have a question. Why do some people fast on keto? What is the purpose of the fasting (intermittent or extended) and is it necessary?

(Robin) #2

welcome! You’ll get tons of input here. There is a special thread happening right now for fasting this month. Or a quick search will bring up lots of info. I think many people slowly transition to some form of fasting, due to natural changes in our appetite as we adapt to keto. I do intermittent… eating between 11AM and 5PM. I didn’t set out with that as a goal. And I don’t time it obsessively. I just lost my old cravings, don’t get hungry till lunch, and feel better if I don’t snack after dinner. I believe it allows my body time to metabolize and rest. I sure sleep better.

But it isn’t necessary. Get your keto groove going strong and then follow your body’s cues. You got this!


Check out some of Dr. Fung’s work. He’s a huge advocate for fasting and its benefits for overall health.

In terms of keto, many here are trying to fix many years of being metabolically unhealthy. Hyperinsulinemia has been purported as the root cause for many of our diseases and metabolical issues. If you aren’t raising insulin, your body processes energy much differently.

(Laurie) #4

Fasting may help with insulin resistance and inflammation, and increase human growth hormone levels – among other things. I don’t know enough about it to say more. It can work well alongside keto, because it offers some of the same benefits. But not all ketoers do it.

(Old Baconian) #5

Welcome to the forums!

Simple answer: not necessary at all.

But many people enjoy fasting, and there are reasons to do so. The first is that it gives the body a chance for the serum insulin level to drop and stay low for a while, which has benefits (insulin does damage when it’s too high, such as stiffening arteries and raising blood pressure, imprisoning fat in adipose tissue, and so forth).

Another reason is to stimulate the cellular repair process known as autophagy (Greek for “self-eating”), in which old and damaged proteins are broken down for re-use. (This is helpful in tightening up loose skin, renewing organ tissue, and so forth).

If you enjoy fasting, have at it. If you don’t enjoy it, don’t fast, and don’t worry about it.

(Juanita Rice) #6

Thank you all for your helpful replies. I understand fasting related to keto much better.


Definitely not necessary, but seems much conducive to keto WOE once you become fat adapted. You don’t eat and you have MORE energy?? Better mental acuity?? :grin:

I tried fasting before keto and I couldn’t do it. However, after being keto for a good length of time, it has been easier to incorporate. I usually can’t make it longer than 24 hours like others can, but setting an intermittent fasting window or time restricted eating plan like fast for 16 hours and eat meals within the other 8 is fairly easy now.

(Doug) #8

I would not go as far as saying ‘not necessary.’ We don’t know, to begin with - there are effects of fasting on possible cancer formation, Alzheimer’s Disease and other neurodegenerative conditions, our immune system, etc., that, at least for a given individual, are or may be highly beneficial.

In the short-term, if there’s nothing that specifically calls for fasting, it’s going to still be an individual thing. Some people find that a keto diet brings overall metabolic healing, while fasting is what really makes them lose fat.

Consuming your own fat - is there a more perfect ketogenic diet than that? However, it’s not totally either/or, fasting or not - even one eating 3 keto meals per day still “fasts” for however long it is between meals, and many, many people lose fat without longer fasts at all.


It’s individual, some people never do IF let alone EF, others find it easy and good after some while. I always did IF, before keto and before I heard about IF. It came naturally and it’s the only type of fasting I like to do. Sometimes I put into a bit more effort but if I get properly hungry or feel some other need to eat, I eat. I am an afternoon eater, I typically am perfectly satiated until 2pm at least.

I do IF because it’s way more convenient and I badly need it to avoid overeating (I almost need one meal a day, I so easily overeat in a big, 5 hour eating window on keto!).
Longer fasts would be for autophagy (and convenience, again. eating is such a chore sometimes and I love eating but it can be a lot of work to satiate me), I can’t list the benefits of autophagy (it’s supposed to be healthy, earlier replacement of worn cells or something? maybe even helps with sagging skin, these come to mind) and it’s a bit mysterious but if it’s no effort or almost none, I like to give it a chance. It’s fun to figure out if we can do it anyway… And may be useful.
Be it EF or IF, fasting while I am in the state of perfect satiation can be quite pleasant, sometimes even blissful :smiley: I surely would hate to eat “all day”! I have most energy when well-fasted. Fasting is really for me. But many people wake up hungry, they should eat. I always woke up definitely NOT hungry, even as a kid, I hated breakfasts so, so much… And now no one can force me to eat in the morning so I can keep my blissful satiated well-fasted state until the afternoon… It’s wonderful.
Keto made my EF skills way worse but IF stayed strong, my eating window even diminished after fat adaptation for a while. Carbs may make my fasting easier (more like longer and more sure as I don’t do hard things in my woe and timing) but typically higher-calories and less pleasant so bad deal. But I never heard about anyone else who had this, people usually talk about lower-carb helping fasting. I didn’t experince that except the help of fat adaptation. I get hungry similarly but my hunger is softer and I can ignore it for a while, it even goes away. So I don’t need to eat immediately when hunger emerges, that was super annoying in my past. Convenience, I love that.

You are knew so for now it’s most important to get used to keto, get comfortable with it. Of course you may fast if you feel like to do it but it’s not some necessity for most people.

I do it in my relaxed way. I eat whenever I feel the need or feel tempted or whatever. It’s usually IF, sometimes 1 meal, sometimes 2, 3 or 5… I try to keep it 1-2 though, much matters on the food choices and waiting for some proper urge.
If whatever you do naturally works, fine. If you feel the need for some change, you may experiment…


Not necessary at all, just something people like, some do it for faster fat loss, some do it for autophagy which is like putting yourself into super repair mode, there’s also links to show it helps with longevity but it’s different for everybody.

(Marianne) #11

I would do a 24-hour fast once a week after I became fat adapted (3-4 months in to clean keto). It wasn’t difficult, but I just didn’t like it. Made me anxious or unsettled, so I said forget it. I haven’t done it since then, although my eating pattern in generally 18-6 (noneating window vs. eating window) per day.

Welcome! Good luck on your journey!

(Bob M) #12

I didn’t start fasting until I had been keto for 1.5 years, but back then (5.5 years ago), it wasn’t a thing until Dr. Fung came along. I then watched all his videos while on vacation and started fasting.

Fasting is a double-edged sword, though. I found it caused me to get too cold after a while, meaning that I was probably lowering my basal metabolic rate. So, it’s possible to overdo.

I still do fasting, though not nearly to the extent I used to. I try one 36 hour fast per week, and not all weeks. I try one 4.5 day fast every once in a while. This year, I’ve only done one long fast, and it was 3.5 days. I’d like to try one more this year.

(Robin) #13

I want to add one reason I won’t be attempting actual fasts, beyond my daily intermittent fasting. I had decades of yo-yo dieting. Feast or famine. I could (and did) go days a without eating. I messed up my body and my thinking process terribly. Those fasts did me no favors, because my overall approach to weight control was totally out of control. So, I wrecked my metabolism. Hence, I feel like the healthiest thing I personally can do for this old body is to be stable, reliable and safe. That’s just me, though.

(UsedToBeT2D) #14

I didn’t fast until about a year on Keto. Then I did a 24 hr, a few weeks later 48 hr. Then a few weeks later a 72 hour fast. The first 48 hours are tough for me, then all of the sudden my body and mind experienced the Zen, My mind was super focused, alert, my body not hungry, an amazing feeling, hard to describe. I’d recommend easing into fasting. But once you get past 48 hours (at least me), you’ll understand. I believe it is therapeutic for mind and body.

(Michael - When reality fails to meet expectations, the problem is not reality.) #15

Short answer: no.

Longer answer: depends. Fasting is just a tool in your new toolbox. What are you trying to accomplish? Where are you now and where do you want to be - could fasting help that process? Folks fast for a number of reasons, some of which have been pointed out already.

Personal anecdote. When I was a child back in the pre-Cambrian era of the 1950s it was very common for folks to eat supper between 5-6PM and breakfast the next morning around 8AM. And little or nothing in between. So breakfast really was ‘breaking the fast’. This was not unusual. So an overnight 12-14 hour fast is not some esoteric keto novelty. In fact it had been the norm for hundreds if not thousands of years. And as already pointed out, eating when you had food and not when you didn’t was a common experience for our ancestors and is likely imprinted quite indelibly in our DNA.

What are the benefits of an overnight fast? At the very least it will pretty much guarantee that you start the next day in ketosis. That’s a good thing. And if you’re already in ketosis because you’re eating keto, it will be even more beneficial because serum glucose and insulin will remain at baseline.

(Doug) #16

Well said, Michael. I’ve only a tiny claim to the 1950s, but the following decade that was my experience too. Dad would get home from work, we’d be home from school, and we’d eat then. An hour or two of playing outside afterwards, plus homework. Sometimes we’d have dessert, but in the course of supper/dinner, not later. So there were those hours of fasting you mentioned - and I’d think that would help with insulin sensitivity and staving off metabolic symdrome/imbalances, regardless of diet.

50 years later I was usually just having coffee in the morning, and often no lunch, so largely eating once per day. IMO this made it much easier to be “fat-adapted;” it was hardly a thing at all for me.

(Joey) #17

Here’s what is necessary: eating.


It’s definitely NOT necessary, but I find that it supercharges keto results. At least it did for me. My main goal was to lose body fat.

I was a guy that would NEVER skip a meal, especially not breakfast. If I did, my memory would be completely shot. I introduced intermittent fasting into my lifestyle and feel great. I can say now that I haven’t had a morning meal this decade. (That sounds cooler in my head then it actually is :slight_smile:)

I can now do fasted workouts, and feel great afterwards. Mind you, I have more than ample fat stores that I can tap into for fuel.

(Juanita Rice) #19

Thank you all for replying. Different opinions are always interesting.

(Rebecca ) #20

You got great answers here! When I began eating Ketogenic (June 2019) the thought of Fasting was horrifying! So I just started with 3 low carb meals daily and felt fine. Then one morning I wasn’t hungry and couldn’t imagine forcing myself to eat so I decided not to, but told myself I’d be ok, and had nuts and cheese on hand at work in case I began to starve (:rofl:) I made it through to lunch! Not long after that, I stopped eating in the evening (as I would sometimes do…just because). So I began Intermittent Fasting naturally…not by decision. I have never done an Extended Fast to-date and don’t think I will…unless my body tells me otherwise! Good luck to you!!!